Recycling of galvanic cells

ABSTRACT

Lithium ion cells in which the cathode contains a particulate insertion material and a binder are cut open in a dry, inert atmosphere ( 10 ). The cell components are treated with a first organic solvent ( 12 ) to dissolve the electrolyte, so that this can be reused. They are then treated with a second organic solvent ( 16 ) to dissolve the binder, and the particulate material separated ( 18 ) from the solution of binder. The insertion material is then reduced ( 22 ) so that it does not contain intercalated lithium. The reduction process may be performed electrolytically.

This application of a 371 of PCT/GB98/03599 filed Dec. 3, 1998.

This invention relates to a process for treating lithium cells and cellcomponents so that component materials can be safely recovered forreuse, particularly but not exclusively for treating rechargeablelithium ion cells in which both the anode and cathode comprise insertionmaterials.

Several of the component materials in rechargeable lithium ion cells arepotentially valuable, so that their recovery and reuse is clearlydesirable. In particular, the cathodes of such cells may contain metaloxides such as lithium cobalt oxide or lithium nickel oxide (or a mixedoxide of the type LiCo_(x)Ni_(1−x)O₂); it may be possible to reuse theseoxides in this form, although it would usually be preferable if theycould be converted to cobalt (II) oxide or nickel (II) oxide (or themixed oxide) not containing intercalated lithium.

Furthermore the electrolyte may contain ingredients such as lithiumtetrafluoroborate or lithium hexafluoro-phosphate which could be reusedin making batteries; the latter material however has poor thermalstability, and undergoes hydrolysis in the presence of water. Canon KKhave described, in EP 0 613 198A, methods for recovering materials fromlithium cells in which an organic solvent is used to dissolveelectrolyte material from the cells, but the cathode active materialalong with polymer binder is merely pulverized.

According to the present invention there is provided a process fortreating cells, each cell including particulate cathode material and abinder, an electrolyte, and an anode material, the process comprisingthe following steps:

a) cutting up the cells in the absence of water;

b) contacting the cells with an organic solvent so as to dissolve outthe electrolyte and any electrolyte solvent;

c) then contacting the cells with a solvent for the binder, and therebyseparating the particulate material; and

d) reducing the particulate cathode material to remove intercalatedions.

The invention also provides a process for treating cell componentscomprising particulate cathode material and a binder, the processcomprising subjecting the cell component to the steps a) and c), andthen performing the step d).

In a preferred method the particulate cathode material is reducedelectrochemically. For example lithium cobalt oxide may be reduced tocobalt (II) oxide, thereby also generating lithium hydroxide. The cellsmay also contain particulate carbon both in the cathode, and as an anodematerial, the anode incorporating the same binder as in the cathode, sothat the particulate material separated in step c) will be a mixture ofcarbon and cathode material; the particulate carbon does not interferewith the electrochemical reduction process, and indeed it may improveit, as it improves the conductivity of the mixed particle bed. In amodification of this method the particulate material iselectrochemically reduced at a circulating particulate bed electrode.

The components of the cells which remain after the two dissolution stepsdescribed above are principally the metal foil current collectors fromthe anode (typically copper) and from the cathode (typically aluminium),the separator, which is typically a non-woven fabric or a micro-porousmembrane of a material such as polypropylene, and any cell casing,insulators and seals. These materials can be separated by their density,and possibly by their magnetic properties.

The cutting up of the cells may be performed using a mechanical cuttingmechanism, or using a laser. This step is preferably performed in aninert atmosphere, which might for example comprise dry nitrogen. Theorganic solvent used in step b) to dissolve out the electrolytepreferably also contains no water, and this dissolution step ispreferably performed at a temperature which does not exceed for example60° C., so that potentially unstable electrolyte salts such as lithiumhexafluoro-phosphate are not degraded. The dissolution processpreferably involves re-circulating the solvent through a vesselcontaining the cut up cells; the solvent may be recirculatedsufficiently vigorously that the cut up cells form a fluidised bed.

The invention will now be further and more particularly described, byway of example only, and with reference to the accompanying drawings inwhich:

FIG. 1 shows a flow chart for the cell treatment process;

FIG. 2 shows, in diagrammatic sectional view, equipment for performingdissolution steps of the process of FIG. 1;

FIG. 3 shows, in diagrammatic sectional view, alternative equipment tothat of FIG. 2;

FIG. 4 shows, in diagrammatic sectional view, equipment for performingan electrochemical reduction step in the process of FIG. 1; and

FIG. 5 shows, in diagrammatic sectional view, alternative equipment tothat of FIG. 4.

In this example a process will be described for recovering componentmaterials from lithium-ion cells which comprise an anode, anelectrolyte, and a cathode, inside a cell casing. The cells may be usedcells, or may be cells rejected during manufacturing. The anode consistsof a copper foil on which is a coating of carbon particles and PVdF as abinder; the cathode consists of an aluminium foil on which is a coatingof lithium cobalt oxide particles, and carbon particles, and PVdF as abinder; the anode and the cathode are separated by a micro-porouspolypropylene membrane containing, as electrolyte, lithiumhexafluoro-phosphate dissolved in an. electrolyte solvent which maycontain ethylene carbonate, propylene carbonate, diethyl carbonate, ordimethyl carbonate for example, or mixtures of these. These are allenclosed in a steel casing.

Referring to FIG. 1, the first step in the process is to cut up thecells in an inert atmosphere and in the absence of water (step 10), sothat in the subsequent steps the solvents can contact the components ofthe cells. This process is desirably carried out in a dry nitrogenatmosphere, and the cutting may be performed using a laser, ormechanical shears for example. The casing is cut open and the othercomponents, which are typically wound into a spiral, are removed. (Inthe process as described here, no further cutting is required at thisstage; in a modification to the process, however, these other componentsare then further cut up or shredded to form small pieces typically onecentimetre square, as described later.)

The spiral wound components (i.e. anode, separator, and cathode) arethen placed in a mesh basket, each spiral being located on a spike, andthe basket is enclosed in a transfer container containing a dry nitrogenatmosphere.

The basket containing the cell components is then transferred to adissolver vessel purged with dry nitrogen, and the basket lowered to thebase of the vessel. In the next step 12, an organic solvent,acetonitrile, is pumped into the dissolver vessel, warmed to 50° C., andrecirculated through the vessel for a few hours to ensure that all theelectrolyte and electrolyte solvent is dissolved. The acetonitrile isthen pumped into an evaporator vessel, the pressure in the vessellowered to below atmospheric pressure (e.g. 10 mm Hg), and the vesselheated to 50 or 60° C. to boil off the acetonitrile (step 14). Theacetonitrile vapour is condensed and can be returned to a storage tank.The solution of electrolyte (lithium hexafluoro-phosphate) inelectrolyte solvent (propylene carbonate etc.) may be stored for reuse(step 15).

NMP (N-methyl-pyrrolidone or 1-methyl-2-pyrrolidone) as a solvent forthe binder is then pumped into the dissolver vessel, warmed to 50° C.,and recirculated through the vessel for a few hours to ensure that allthe binder has dissolved (step 16). The NMP containing the PVdF insolution and the particulate material in suspension is then drained outof the dissolver vessel and passed through a filter (step 18). Thefiltrate is pumped into an evaporator vessel, the pressure in the vesselmay be lowered to below atmospheric pressure, and the vessel heated tosay 90° C. to boil off the NMP (step 20). The NMP vapour is condensedand can be returned to a storage tank for subsequent use in thedissolver vessel.

The filter is then back-washed with water and the suspension ofparticulate material (lithium cobalt oxide and carbon) in watertransferred to an electrolysis cell. The filter is then dried withnitrogen gas before reuse. In the electrolysis cell the lithium cobaltoxide is subjected to electrolytic reduction adjacent to the cathode ofthe cell, the cell electrolyte being a solution of lithium hydroxide inwater (step 22), to form cobalt (II) oxide, and increasing theconcentration of the lithium hydroxide solution. The reaction can berepresented by the equation:

e⁻+H₂O+LiCo(III)O₂→Co(II)O +Li⁺+2OH⁻

Finally, at step 24, the lithium hydroxide solution is decanted from thecell and the cobalt oxide and carbon mixture is washed (step 25) andremoved for storage. It should be noted that although the carbon mayinitially contain intercalated lithium ions, these come out intosolution when the carbon is in contact with water or aqueous lithiumhydroxide solution without the need for any chemical treatment.

The solid materials remaining in the dissolver, i.e. copper foil,aluminium foil, and micro-porous plastic sheet, are then removed and canbe sorted for storage (step 26). One way in which this may be performedis to shred the materials (if this has not been done already) and thenseparate them according to their densities. If steel is also present, itmay be separated by its magnetic properties.

Referring now to FIG. 2, there is shown a dissolver vessel 30 suitablefor performing the dissolution steps 12 and 16 described above. Thevessel comprises a domed lid or upper portion 32 and a generallycylindrical lower portion with a curved base 34 which are sealed to eachother at a flanged joint 35. The upper portion 32 encloses a mesh basket36 above a base plate 38 which are both supported by a slide rod 40which projects through a seal 42, the base plate 38 sealing to an innerflange 39, while the basket 36 is being transferred from the cutting upstation (not shown) to the dissolver vessel 30; and after the upperportion 32 has been joined to the lower portion 34 the basket 36 alongwith the base plate 38 are lowered into the lower part of the lowerportion 34 as shown. The lower portion 34 is provided with severalvalved inlets or outlets as follows: an inlet 44 for dry nitrogen, anoutlet 45 connected to a gas extracting vent; an inlet 46 foracetonitrile, an outlet 47 in the base for acetonitrile, and a pressureequalisation duct 48 connected to the acetonitrile evaporator vessel(not shown); an inlet 49 for NMP, an outlet 50 in the base for NMP, anda pressure equalisation duct 51 connected to the NMP evaporator vessel(not shown); an inlet 52 for water and an outlet 53 in the base forwater. The lower portion 34 is also provided with trace electricalheating 54 so that it its contents may be warmed to for example 50° C.

Thus in operation the upper portion 32 enclosing the basket 36 is sealedto the lower portion 34, and the lower portion 34 is thoroughly dried bypurging with dry nitrogen via the inlet 44 and the outlet 45; the basket36 is then lowered into the position shown. Acetonitrile is thencirculated through the vessel 30, which is held at 50° C., via the inlet46 and outlet 47; after three or four hours the inlet 46 is closed, thepressure equalisation duct 48 is opened, and the acetonitrile is pumpedvia the outlet 47 to the evaporator vessel. NMP is then circulatedthrough the vessel 30, which is still held at 50° C., via the inlet 49and outlet 50; after three or four hours the inlet 49 is closed, thepressure equalisation duct 51 is opened, and the NMP is pumped via theoutlet 50 to the NMP evaporator vessel. Any remaining water-solublesalts can then be removed by washing with water via the inlet 52 and theoutlet 53.

It will be appreciated that the dissolution steps 12 and 16 mightinstead be performed in a different vessel. For example the cells mightbe shredded, either along with the casings or after removal of thecasings, for example into pieces about 1 cm square, which might beprocessed in a fluidised bed vessel as shown in FIG. 3 to whichreference is now made. The shredded pieces are fed via a hopper 55 intoa dissolution chamber 60 defined between lower and upper mesh screens62. An organic solvent such as acetonitrile is then circulated by a pump63 and a duct 64 sufficiently vigorously that the pieces in thedissolution chamber 60 become fluidised. This may enable fasterdissolution rates to be achieved than the dissolver vessel 30 describedin relation to FIG. 2. When the dissolution process has been completed,the pieces can be removed via an exit duct 66.

Referring now to FIG. 4 there is shown a cell 70 for the electrolyticreduction of the lithium cobalt oxide (step 22 in FIG. 1). The cell 70comprises a generally cylindrical, plastic-lined steel vessel 72 with aflat base. On the base is a carbon electrode 74 whose upper surfaceslopes towards a central shallow recess 75. A lid 76 carries aplatinized titanium electrode 78 and inlets and outlets as follows: aninlet 80 for lithium hydroxide solution, an inlet 81 for water andparticles of carbon and lithium cobalt oxide from the filter (notshown), an outlet duct 82 for lithium hydroxide solution which extendsto a position well above the electrode 74, an outlet duct 83 for lithiumhydroxide solution and treated particles, which extends into the centralrecess 75, and an outlet duct 84 for any gases generated duringelectrolysis.

In operation a mixture of carbon and lithium cobalt oxide particleswashed off the filter by a stream of water flows into the cell 70 viathe inlet 81 and settles out to form a bed on the electrode 74. Aqueouslithium hydroxide solution is supplied via the inlet 80 so the liquidlevel is above the electrode 78. A voltage of about 2.0 volts is thenapplied between the carbon electrode 74 as cathode and the otherelectrode 78 as anode, the voltage being such as to restrict hydrogengeneration, and electrolysis is continued until the electric currentdecreases significantly. This indicates that the electrolytic reductionof the lithium cobalt oxide has been substantially completed. Theelectric current is then stopped, and most of the lithium hydroxideelectrolyte in the cell is extracted through the duct 82 (whose open endis slightly above the top of the particle bed). The remaining lithiumhydroxide solution along with all the particles are then extracted viathe duct 83 to a filter (not shown). The particles of carbon and cobalt(II) oxide can then be washed off the filter with water, and stored forreuse.

It will also be appreciated that this electrolytic production processmight be carried out in a different cell, for example a fluidised bed,or a divided cell 90 with a circulating particle bed electrode 92 as itscathode, as shown diagrammatically in FIG. 5 to which reference is nowmade. In the cell 90 a membrane 93 separates the anolyte region 94 fromthe catholyte region 95, and these are inclined at an angle to thevertical. A platinized titanium electrode 96 is provided as the anode,and an anolyte such as aqueous lithium hydroxide is passed through theregion 94. A carbon cathodic plate 97 forms the rear surface of theregion 95 and a catholyte, which may also be lithium hydroxide solution,is pumped upwardly through the catholyte region 95 between an inlet 98and an outlet 99; the particles are introduced into the catholyte region95, and the electrolyte flow is sufficiently vigorous that the particlescirculate upwardly adjacent to the membrane 93, and then downwardly as aflowing packed bed 92 over the cathode plate 97. A voltage of about 1.75volts is applied between the electrodes 96 and 97, and lithium cobaltoxide is reduced to cobalt (II) oxide. Such a circulating particle bedelectrode is described by F. Goodridge et al (Electrochim. Acta 22(1977) 1087), and in U.S. Pat. Nos. 3,945,892 and 3,981,787 (G.S. Jameset al).

It will be appreciated that the process of the invention may be modifiedin various ways. For example if the electrolyte solvent obtained at step15 is a mixture, for example containing diethyl carbonate, dimethylcarbonate and propylene carbonate, then the first two (DEC and DMC) canbe extracted by distillation at reduced pressure.

It will also be appreciated that the process is equally applicable tolithium ion polymer cells, which have a polymer electrolyte in place ofthe separator and liquid electrolyte. If the polymer electrolytecontains PVdF then it will be dissolved out by the NMP along with theelectrode binder (at step 16). If it contains a different polymer thenthe solvents would have to be selected accordingly.

What is claimed is:
 1. A process for treating cell components comprisingparticulate cathode material and a binder, the process comprising thefollowing steps: a) cutting up the cell components in an inertatmosphere and in the absence of water; b) then contacting the cellcomponents with a solvent for the binder, and thereby separating theparticulate material; and c) reducing the particulate cathode materialto remove intercalated ions.
 2. A process as claimed in claim 1 whereinthe particulate cathode material is reduced electrochemically.
 3. Aprocess as claimed in claim 2 wherein the particulate material iselectrochemically reduced at a circulating particulate bed electrode. 4.A process as claimed in claim 1 wherein the dissolution process involvesre-circulating the solvent through a vessel containing the cut up cellcomponents.
 5. A process as claimed in claim 4 wherein the solvent isrecirculated sufficiently vigorously that the cut up cell componentsform a fluidised bed.
 6. A process for treating cells, each cellincluding particulate cathode material and a binder, an electrolyte, andan anode material, the process comprising the following steps: a)cutting up the cells in an inert atmosphere and in the absence of water;b) contacting the cells with an organic solvent so as to dissolve outthe electrolyte and any electrolyte solvent; c) then contacting thecells with a solvent for the binder, and thereby separating theparticulate material; and d) reducing the particulate cathode materialto remove intercalated ions.
 7. A process as claimed in claim 6 whereinthe particulate cathode material is reduced electrochemically.
 8. Aprocess as claimed in claim 7 wherein the particulate material iselectrochemically reduced at a circulating particulate bed electrode. 9.A process as claimed in claim 6 wherein at least one dissolution processinvolves recirculating the solvent through a vessel containing the cutup cells.
 10. A process as claimed in claim 9 wherein the solvent isrecirculated sufficiently vigorously that the cut up cells form afluidised bed.